High alloy steel

ABSTRACT

DESCRIBED HEREIN IS A COMPOSITION CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT, 16-25% CHROMIUM, 10-22% NICKEL, 4-10% MOLYBDENUM, UP TO 0.08% CARBON, UP TO 2.0% MANGANESE, UP TO 1.5% SILICON AND THE BALANCE ESSENTIALLY IRON AND STEEL MAKING RESIDUALS.

United States atent 3,716,354 HIGH ALLUY STEEL Orville W. Reen, LowerBurrell, Pa, assignor to Allegheny Ludlum Industries, Inc, Pittsburgh,Pa. No Drawing. Filed Nov. 2, 1970, Ser. No. 86,358 Int. Cl. CZZc 39/20,39/50 US. Cl. 75128 W Claims ABSTRACT OF THE DISCLOSURE Described hereinis a composition consisting essentially of, in weight percent, 16-25%chromium, -22% nickel, 4-l0% molybdenum, up to 0.08% carbon, up to 2.0%manganese, up to 1.5% silicon and the balance essentially iron and steelmaking residuals.

Stainless steel has been frequently used in applications requiringresistance to corrosion in environments involving exposure to chlorideand chlorine ions. Commonly used materials for these applications havebeen high alloy stainless steels such as type 316 and type 3161.. Suchhigh alloyed compositions, however, suffer from the disadvantage thatthey are difficult to hot work and as a result pose serious fabricationproblems.

In some cases it has been suggested to utilize powder metallurgicaltechniques to produce articles of high alloy stainless steel to avoidthe aforementioned fabrication difficulties which may be associated withsuch materials.

However, because of their porous nature, pressed and sintered stainlesssteel powder articles are particularly subject to corrosive attack as aresult of susceptibility to crevice corrosion. Even such high alloyedmaterials as type 316 and type 316L prove inadequate in pressed andsintered articles when exposed to corrosion testing. This is evidencedby the failure of sintered parts of type 316L to withstand 100 hoursexposure in 5% neutral sodium chloride spray without rusting. Thisrusting has been found to occur at all levels of density up to, but notincluding, 100% and is attributed to the presence of pores in thesurface. It is evident that there is a need for stainless steelcompositions which, when manufactured into articles from powder metal,will provide more resistance to corrosive environments such as thechlorine ion than that of type 316L steels and possess improvedresistance to crevice corrosion as a pressed and sintered article.

The present invention provides a novel composition which avoids theaforementioned difiiculties associated with powder metal partsmanufactured of presently available high alloy steel powders. Inaccordance with the invention there is provided a composition consistingessentially of, in weight percent, up to 0.08% carbon, preferably up to0.03%; up to 2.0% manganese, preferably up to0.3%; up to 1.5% silicon,preferably 0.6 to 1.25%; 16 to 25% chromium, preferably 17 to 25%; 10 to22% nickel, preferably 14 to 22%; 4 to 10% molybdenum, preferably 47%;and the balance essentially iron and the usual steel making residuals.Alloys, in accordance with the invention, may be melted and atomizedinto pre-alloyed powder and then pressed and sintered into powder metalcomponents of greater corrosion resistance than possessed by the mosthighly alloyed commercially available stainless steel powder, e.g., type316L. The minimum values of the alloying elements chromium, nickel andmolybdenum, in the foregoing broad range have been found to be theminimum amounts necessary to obtain satisfactory corrosion resistancefor these alloys in powder articles. However, no significant improvementis observed beyond the maximum values. For commercial powdermetallurgical operations, it is desirable to utilize irregularly shapedparticles. The preferred limits of 0.3% maximum manganese and at least0.6% silicon are established to maximize the desirable particleconfiguration.

The following examples illustrate the practice of the invention and thesuperior properties obtainable thereby.

Atomized powders of the compositions described in Table I were preparedand screened to a size suitable for powder metal processing (about 0.149mm. and finer), having the characteristics described in Table II.Thereafter they were pressed into compacts and sintered in dry hydrogenat temperatures of 2000 to 2200 F. The sintered compacts were about toof their full density. A commercial type 316L powder was pressed andsintered in a similar fashion.

TABLE I P S S1 Cr Ni Mo Fe O. 008 0. 005 1. 05 17. 97 10. 22 4. 92Balanc 1.014 0.008 0.80 16.85 12.78 2.34 Do. 0.010 0.004 0.95 18.0512.20 4.80 Do. 0. 003 0.003 0.81 17.65 15.05 3.07 Do. 0.008 0.006 0.7917.69 14. 05 4.02 Do. 0.012 0.004 0.86 17. 74 15.00 5.05 D0. 0.008 0.0030.90 17. 92 14. 90 7.05 D0. 0.013 0.003 0.84 17.75 19.86 6.96 D0. 0.0100.011 0.74 21. 16 12. 08 4.00 Do. 0. 015 0.008 0.76 21.40 12.80 5.00 Do.0.015 0.007 0.70 20.88 21.60 7.30 Do. 0.018 0.013 0.71 24.08 20.88 4.00D0.

TABLE II Properties of Atomized Pre-Alloyed Powders Mesh sizedistribution, wt. percent Flow, Apparent seeonds/ density, Run No100/+200 200/+325 325 50g gJcu. cm

1 ASTM Method 13213-48. 2 ASTM Method 13212-48.

The pressed and sintered compacts of the compositions disclosed in TableI were exposed to the following corrosive environments:

(1) neutral NaCl spray (2) Immersion in aqueous solutions of 5, 10, and20 weight percent NaCl.

(3) Immersion in aqueous solutions of 5, and

weight percent NI-I Cl.

of atmospheres may be used. In addition the density of the compactsproduced may vary depending upon the nature of the article manufactured.

I claim:

1. An atomized, prealloyed powder consisting essentially of, in weightpercent, up to 0.08% carbon, up to 0.3% manganese, 0.6 to 1.25% silicon,16 to chromium, 10 to 22% nickel, 4 to 10% molybdenum and the balanceessentially iron and steel making residuals.

2. An atomized, prealloyed powder according to claim 1 having 4 to 7%molybdenum.

3. An atomized, prealloyed powder according to claim 1 having 17 to 25%chromium.

4. An atomized, prealloyed powder according to claim 1 having 14 to 22%nickel.

5. An atomized, prealloyed powder according to claim 1 having up to0.03% carbon, 17 to 25% chromium, 14 to 22% nickel and 4 to 7%molybdenum.

TABLE III Corrosion Test; Results of Pressed and Sintered AtomizedPre-Alloyed Powders 100 hour Qast. Smtered Percent exposure to Hours torust when immersed in aqueous solutions ofdensity, density, of east 5%neutral Run No. gJcu. em. g Icu. cm. density salt spray 1 5% N 9.01 10%NaCl 20% N 2.01 5% NH4C1 10% NHlCl 20% NHrCl 416 7. 88 5. 95 75. 5 504N.R 168 504 N.R. 504 N.R. 48. Commercial T316". 2 7. 90 6. 28 79. 5 24 3504 N.R 24 3. 418 7. 97 5. 6G 71. 0 168 24 504 N.R 504 N.R. 24. 7. 97 5.S3 73. 2 528 N.R. 96 504 N.R 504 N.R. 06. 7.98 5. 85 73. 3 528 N.R. 600N.R. 504 N.R 528 N.R 7. 99 6. 02 75. 3 504 N.R. 168 504 N.F 504 N.R 24.8. 01 5. 61 70.0 528 N.R. 600 N.R. 504 N.R 528 N.R 528 N.R 8.02 5. 6770.7 528 N.R. 600 N.R. 504 N.R 504N.R 504N.R 7. 91 5. 68 71. 8 504 N.R.24 504 N.R 504 N.R 24. 7. 86 5. 54 70.5 504 N.R. 168 504 N.R 504 N.R 24.8. 04 5. 69. 7 528 N.R. 600 N.R 504 N.R 504 N.R 504 N.R 7.81 5.50 70.4528 N.R. 600 N.R 504 N.R 504N.R 504 N.R 7.93 5.44 68.6 504 N.R. 600 N.R504 NJ?! 504 N.R 504 N.R

l ASTM Method B117. 9 Published value.

NOTE.-N.R.=NO rust.

References Cited UNITED STATES PATENTS 2,819,161 1/1958 Cupler 1263,547,625 12/ 1970 Bieber, et al. 75-128 2,872,311 2/ 1959 Marshall75200 3,334,999 8/ 1967 Naeser 75-200 X 3,425,813 2/ 1969 Orlemann75--0.5 BA X 3,520,680 7/ 1970 Orlemann 75-200 X OTHER REFERENCES MetalsHandbook, 8th Edition, Vol. 1, Properties and Selection of Metals,American Society for Metals, Metals Park, Ohio, pp. 408 and 409.

L. DEWAYNE RUTLEDGE, Primary Examiner I. LEGRU, Assistant Examiner US.Cl. X.R.

750.5 BA, 0.5 C

